Method and apparatus for performing hydrogen optical emission endpoint detection for photoresist strip and residue removal

ABSTRACT

Methods for monitoring and detecting optical emissions while performing photoresist stripping and removal of residues from a substrate or a film stack on a substrate are provided herein. In one embodiment, a method is provided that includes positioning a substrate comprising a photoresist layer into a processing chamber; processing the photoresist layer using a multiple step plasma process; and monitoring the plasma for a hydrogen optical emission during the multiple step plasma process; wherein the multiple step plasma process includes removing a bulk of the photoresist layer using a bulk removal step; and switching to an overetch step in response to the monitored hydrogen optical emission.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 10/776,672, filed Feb. 11, 2004, which claims benefit of U.S.provisional patent application Ser. No. 60/447,625, filed Feb. 15, 2003.Each of the aforementioned related patent applications is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method for semiconductorsubstrate processing. More specifically, the invention relates to amethod for monitoring and detecting optical emission endpoint(s), forphotoresist stripping and removal of residues from a substrate or a filmstack on a substrate.

2. Description of the Related Art

As a part of semiconductor manufacturing, various layers of dielectric,semiconducting, and conducting films, such as silicon dioxide,polysilicon, and metal compounds and alloys, are deposited on a siliconsubstrate. Features are defined in these layers by a process includinglithography and etching. Such a process comprises coating a substratewith photoresist, patterning the photoresist, and then transferring thispattern to the underlying layers during etching by using the patternedphotoresist as an etch mask. Many of these etch processes leavephotoresist and post-etch residues on the substrate and must be removedbefore performing the next process step.

Patterned photoresist also serves as an ion implant mask forpreferentially doping semiconductor substrates in selected areas. Thedoping or implantation process includes exposing the substrate to ionsor an electronic beam of implant species, for example, arsenic (As),boron (B, BF₂, BF₄), phosphorous (P), indium (In), antimony (Sb) andhydrogen (H). The ion implantation process dehydrogenates thephotoresist material, resulting in a hydrogen deficient, carbonizedcrust layer that is typically one to several thousand angstroms thick ontop of the bulk photoresist. This makes the characteristics of thephotoresist material vertically non-uniform such that uniform removal(stripping) of the photoresist can be difficult. As such, thephotoresist removal process may result in non-uniform removal andsubstantial post-implant residue remaining on the substrate.Consequently, a technique for monitoring removal of the photoresist isnecessary such that the photoresist removal process can be controlled asthe characteristics of the material change.

Optical emission spectroscopy is commonly used to detect the endpoint ofplasma etch processes. Plasma transitions of reactant or by-productspecies emit photons which can be detected in the ultraviolet, visibleand near-infrared ranges. Thus, the endpoint is usually based onincreasing signal for reactants or decreasing signal for by-products.The endpoint is identified when either the reactants or by-productsattain a specific concentration (i.e., the respective signals cross athreshold level). However, such an endpoint detection technique does notaccount for the variations in the characteristics of a photoresist layerthat has been exposed to an ion beam.

Therefore, there is a need in the art for a method and apparatus forperforming optical emission endpoint detection for photoresist strip andresidue removal especially when using a chamber having a remote plasmasource.

SUMMARY OF THE INVENTION

The invention relates to a method for monitoring and detecting opticalemission endpoint(s), more particularly hydrogen emissions within aplasma, for photoresist stripping and removal of residues from asubstrate or a film stack on a substrate. In one embodiment, a method isprovided that includes positioning a substrate comprising a photoresistlayer into a processing chamber; processing the photoresist layer usinga multiple step plasma process; and monitoring the plasma for a hydrogenoptical emission during the multiple step plasma process; wherein themultiple step plasma process includes removing a bulk of the photoresistlayer using a bulk removal step; and switching to an overetch step inresponse to the monitored hydrogen optical emission.

In another embodiment, a method is provided that includes positioning asubstrate comprising a photoresist layer into a processing chamber;processing the photoresist layer using a multiple step plasma process;and monitoring the plasma for both by-product optical emission and areactant optical emission during the multiple step plasma process;wherein the multiple step plasma process includes removing a bulk of thephotoresist layer using a bulk removal step; and switching to anoveretch step in response to the monitored hydrogen optical emission.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIGS. 1A and 1B is an illustrative graph of a hydrogen emission peak fora blanket photoresist and an arsenic implanted photoresist;

FIG. 2 is an illustrative graph of a hydrogen emission peak for threearsenic implanted substrates during a substrate test showingrepeatability of an hydrogen emission peak;

FIG. 3 is a flow diagram of one embodiment of a method of the presentinvention;

FIGS. 4A-B are illustrative graphs of hydrogen and oxygen emissiontraces for stripping of unimplanted photoresist (FIG. 4A), arsenicimplanted photoresist (FIG. 4B), phosphorous implanted photoresist (FIG.4C) and boron implanted photoresist (FIG. 4D); and

FIG. 5 is a schematic diagram of one embodiment of an illustrativechamber used to perform the method of the present invention.

DETAILED DESCRIPTION

The invention relates to a method for monitoring and detecting opticalemission endpoint(s), more particularly hydrogen emissions, forphotoresist stripping and removal of residues from a substrate or a filmstack on a substrate. In one embodiment of the invention, a methoddetermines and uses a hydrogen optical emission peak for identifying anendpoint of a photoresist stripping process, including blanket andpatterned photoresist, post-implant photoresist, and post-plasma etchphotoresist. In addition, the invention comprises a method to useoptical emission endpoint in general, and hydrogen peak specifically, tomonitor the transition from crust removal to bulk photoresist removalfor post-implant stripping. By this method, the hydrogen endpoint traceis a more direct measure of stripping for patterned implant substrates(compared to other peaks such as oxygen).

The present invention uses, in one embodiment, the hydrogen opticalemission peak at 656 nm to monitor endpoint for ion implant strip, andcan be applied to other reducing chemistry based stripping processes forstrip and residue removal after the etching of low dielectric constantfilms (low k films), and for other applications.

For the crust removal process in post-implant strip, the hydrogen signalcan be especially useful because the crust layer is hydrogen-depletedrelative to the bulk photoresist. Thus, in accord with an embodiment ofthe present invention, monitoring for the rise and leveling-off of thehydrogen peak (656 nm) indicates that the hydrogen-depleted crust layeris removed and that the hydrogen-rich bulk photoresist has been reached.The ability to accurately identify the crust removal clearing time is ofuse for identifying changes in substrate conditions or in situationswhere a multi-step stripping recipe is beneficial.

FIGS. 1A-B depict the hydrogen emission trace that occurs during removalof an unimplanted photoresist layer (FIG. 1A) and arsenic implantedphotoresist layer (FIG. 1B). The graphs 100 and 102 depict emissionintensity (axis 104) versus time (axis 106). During the stripping ofphotoresist from the unimplanted substrate, the hydrogen emission trace108 increases (portion 110) then levels off (portion 112), and thendecreases (portion 114), allowing endpoint detection as the photoresistclears. For the implanted substrate, the clearing of the crust layer canbe easily identified in trace 116. The crust layer is hydrogen deficientas described above, such that the hydrogen emission is low at thebeginning of the stripping process (portion 118). As the crust isremoved, the hydrogen emission increases (portion 120) until a plateauis reached (122). Finally, the bulk photoresist is removed and thehydrogen emission decreased (portion 124). The repeatability of thehydrogen emission peak during a 100 substrate run with implanted blanketphotoresist monitor substrates is evident in the emission graphs forsubstrates 2, 49, and 99 shown in FIG. 2.

One advantage of the present invention is that the hydrogen signal iscreated as a process by-product, rather than a process reactant likeoxygen. Thus, the change in optical emission signal is a more directmeasure of the photoresist removal process, as opposed to a processreactant which is more of an indirect measure of photoresist removal andmay also include additional reactions not related to the photoresistremoval process (such as reactions with residues on chamber walls orother locations other than the substrate). A by-product peak should beless sensitive to non-uniformity issues, which, for the bulk strip stepof post-implant strip, could lead to overly-short process times. Whileother by-product signals may also be used to signal the end of the crustremoval (e.g., the OH peak at ˜311 nm), the hydrogen signal issignificantly stronger in intensity and more well-defined than any ofthese other peaks and therefore provides a clearer endpoint trace. Inaddition, when using of the hydrogen peak over the OH peak, it may beadvantageous if water vapor is used in the recipe, where the water vapormay mask the OH peak.

Furthermore, as a process by-product, the hydrogen emission can bemonitored near the substrate surface in a remote plasma source reactoras described with respect to FIG. 5 below.

FIG. 3 is a flow diagram of a method 300 of the present invention. Themethod begins at step 302 and proceeds to step 304 where a substrate ispositioned in a process chamber capable of performing photoresiststripping. One such chamber is manufactured under the trademark AXIOM™by Applied Materials, Inc. and described with respect to FIG. 5 below.

At step 306, the method performs a plasma process in the strip chamber.To remove photoresist, an oxygen-based plasma is used. For example, anoxidizing gas such as O₂, is applied to a remote plasma source at a flowrate of 100 to 10,000 sccm. The oxidizing gas is formed into a plasmawhen 600 to 6000 watts of RF energy is applied to the source. The gaspressure in the chamber is maintained at 0.3 to 3 Torr. The temperatureof the substrate is maintained at 15 to 300 degrees Celsius. In oneembodiment of the invention, an RF bias of 100 to 2000 watts is appliedto the substrate. Various oxidizing gases can be used including, but notlimited to, O₂ O₃, N₂O, H₂O, CO, CO₂, alcohols, and various combinationsof these gases. In other embodiments of the invention, nonoxidizinggases may be used including, but not limited to, N₂, H₂O, H₂, forminggas, NH₃, CH₄, C₂H₆, various halogenated gases (CF₄, NF₃, C₂F₆, C₄F₈,CH₃F, CH₂F₂, CHF₃), combinations of these gases and the like.

At step 308, the method 300 monitors the hydrogen emission within theplasma in the chamber. At step 310, the method responds to the emissionmagnitude. In one embodiment, the chamber parameters, (e.g., gases,power levels, pressure, temperature and the like) may be altered upondetecting a change in the hydrogen emission. As such, the emission canbe used to optimize processing or to cease processing when thephotoresist is removed. Alternatively, one chemistry or recipe can beused for photoresist crust removal and a second chemistry or recipe canbe used for bulk photoresist removal. Similarly, the bulk photoresistcan be removed until another emission change occurs, then a thirdchemistry or recipe can be used to remove residue that remains from thestripping process. The method 300 ends at step 312.

In another embodiment of the present invention, a method uses acombination of a hydrogen optical emission with one (or more) additionalemission peak(s) for more robust and/or flexible endpoint control. Assuch, step 308 can be used to monitor other emissions (shown inphantom).

The use of the by-product hydrogen signal in combination with otheroptical emission peaks can provide several advantages. For example, thereactant oxygen signal provides multiple indicators of stripping thoughtransition layers between the crust and bulk photoresist. Also, themethod of the present invention permits identification of an earlyendpoint indicator by monitoring the reactant oxygen peak and alate/final indicator by monitoring the by-product hydrogen peak. FIGS.4A-B depicts graphs hydrogen and oxygen optical emission traces duringthe stripping of blanket unimplanted (graph 400), arsenic implantedphotoresist (graph 420), as well as phosphorous (graph 440) and boron(graph 460) implanted photoresist. Each graph depicts emission magnitude(axis 404) versus time (axis 406). In graph 400, the hydrogen emissionis trace 408 and the oxygen emission is trace 410 and, in graph 420, thehydrogen emission is trace 418 and the oxygen emission is trace 416. Ingraph 440, the hydrogen emission is trace 436 and the oxygen emission istrace 438 and, in graph 460, the hydrogen emission is trace 456 and theoxygen emission is trace 458. These data show that the implant speciesand conditions vary the specific intensity versus time values, but thatthe general shape of the emissions traces is the same, allowing for useof the method described herein. In this example of an embodiment of thepresent invention, the hydrogen and oxygen signals mirror each othersince the hydrogen is a by-product peak and oxygen is a reactant peak.By measuring and monitoring both wavelengths, the method can incorporatecustom endpoint algorithms to minimize risk of mis-processing andmaximize throughput by optimizing process duration. In addition,utilization of the present invention can drastically reduce errors byproviding a back-up wavelength. In other words, using both signals,simultaneously allows for more robust endpoint capability by providing abackup detection wavelength—if the endpoint is missed at one wavelength,the endpoint can be triggered by the other wavelength. Dual wavelengthendpoint triggering occurs when either wavelength meets the endpointconditions.

The dual wavelength optical emission can provide advantages for otherprocesses, such as post-silicon etch photoresist strip and residueremoval, where the process is switched at step 310 of FIG. 3 from resiststripping chemistry to residue removal and/or softening chemistry as thephotoresist removal is detected. The combination of the reactant oxygenand by-product hydrogen signals is most useful for controlling theplasma-on time for photoresist removal. Because residues are sometimesmore difficult to remove when exposed to excessive oxygen radicals,inaccurate endpoint control can result in overly-long plasma-on times toensure complete photoresist removal, which in turn reduces the efficacyof residue removal post-treatments. Accurate endpoint control limits theoxidizing plasma exposure, thereby increasing the effectiveness ofresidue-removal post-treatments.

The present inventive method may be used on a variety of systems as thehardware requirements for the implementation of this invention are notunique. FIG. 5 depicts a schematic diagram of the AXIOM™ reactor (orchamber) 500 that may be used to practice portions of the method 300.The AXIOM reactor 500 is described in detail in U.S. patent applicationSer. No. 10/264,664, filed Oct. 4, 2002 and incorporated herein byreference. The reactor 500 comprises a process chamber 502, a remoteplasma source 506, and a controller 508.

The process chamber 502 generally is a vacuum vessel, which comprises afirst portion 510 and a second portion 512. In one embodiment, the firstportion 510 comprises a substrate pedestal 504, a sidewall 516 and avacuum pump 514. The second portion 512 comprises a lid 518 and a gasdistribution plate (showerhead) 520, which defines a gas mixing volume522 and a reaction volume 524. The lid 518 and sidewall 516 aregenerally formed from a metal (e.g., aluminum (Al), stainless steel, andthe like) and electrically coupled to a ground reference 560. Thesidewall comprises a window 594 (quartz) that is used to monitor theoptical emissions within the plasma. The window 594 is coupled to alight-collecting device 592 that carries the optical signals to theoptical emission spectroscopy (OES) system 590.

The substrate pedestal 504 supports a substrate (wafer) 526 within thereaction volume 524. In one embodiment, the substrate pedestal 504 maycomprise a source of radiant heat, such as gas-filled lamps 528, as wellas an embedded resistive heater 530 and a conduit 532. The conduit 532provides cooling water from a source 534 to the backside of thesubstrate pedestal 504. The substrate sits on the pedestal by gravityor, alternatively, can be mechanically clamped, vacuum clamped, orelectrostatically clamped as in an electrostatic chuck. Gas conductiontransfers heat from the pedestal 504 to the substrate 526. Thetemperature of the substrate 526 may be controlled between about 20 and400 degrees Celsius.

The vacuum pump 514 is adapted to an exhaust port 536 formed in thesidewall 516 of the process chamber 502. The vacuum pump 514 is used tomaintain a desired gas pressure in the process chamber 502, as well asevacuate the post-processing gases and other volatile compounds from thechamber. In one embodiment, the vacuum pump 514 is augmented with athrottle valve 538 to control the gas pressure in the process chamber502.

The process chamber 502 also comprises conventional systems forretaining and releasing the substrate 526, internal diagnostics, and thelike. Such systems are collectively depicted in FIG. 5 as supportsystems 540.

The remote plasma source 506 comprises a power source 546, a gas panel544, and a remote plasma chamber 542. In one embodiment, the powersource 546 comprises a radio-frequency (RF) generator 548, a tuningassembly 550, and an applicator 552. The RF generator 548 is capable ofproducing of about 200 to 5000 W at a frequency of about 200 to 600 kHz.The applicator 552 is inductively coupled to the remote plasma chamber542 and energizes a process gas (or gas mixture) 564 to a plasma 562 inthe chamber. In this embodiment, the remote plasma chamber 542 has atoroidal geometry that confines the plasma and facilitates efficientgeneration of radical species, as well as lowers the electrontemperature of the plasma. In other embodiments, the remote plasmasource 506 may be a microwave plasma source, however, the strippingrates are generally higher using the inductively coupled plasma.

The gas panel 544 uses a conduit 566 to deliver the process gas 564 tothe remote plasma chamber 542. The gas panel 544 (or conduit 566)comprises means (not shown), such as mass flow controllers and shut-offvalves, to control gas pressure and flow rate for each individual gassupplied to the chamber 542. In the plasma 562, the process gas 564 isionized and dissociated to form reactive species.

The reactive species are directed into the mixing volume 522 through aninlet port 568 in the lid 518. To minimize charge-up plasma damage todevices on the substrate 526, the ionic species of the process gas 564are substantially neutralized within the mixing volume 522 before thegas reaches the reaction volume 524 through a plurality of openings 570in the showerhead 520.

The controller 508 comprises a central processing unit (CPU) 554, amemory 556, and a support circuit 558. The CPU 554 may be any form of ageneral-purpose computer processor used in an industrial setting.Software routines can be stored in the memory 556, such as random accessmemory, read only memory, floppy or hard disk, or other form of digitalstorage. The support circuit 558 is conventionally coupled to the CPU554 and may comprise cache, clock circuits, input/output sub-systems,power supplies, and the like.

The software routines, when executed by the CPU 554, transform the CPUinto a specific purpose computer (controller) 508 that controls thereactor 500 such that the processes (e.g., method 300 of FIG. 3) areperformed in accordance with the present invention. The softwareroutines may also be stored and/or executed by a second controller (notshown) that is located remotely from the reactor 500.

The AXIOM™ chamber has a window port 594 for attaching alight-collecting device 592 (e.g., a fiber optic probe and cable) tomonitor plasma intensity. The window is located slightly above thesubstrate plane for collecting emission intensity along a line parallelto the substrate. Optical emission spectroscopy hardware 590 based oneither a monochromator that can be set to monitor the emission (abovethe substrate) of a particular wavelength within the entire spectrum orhardware based on bandwidth filter(s), or even a spectrometer, can beused. An exemplary embodiment of the present invention may use adetector unit with two bandpass filters on the chamber. In such anembodiment, one of the filters includes the 656 nm emission, or hydrogenoptical emission peak, wavelength.

In addition to process control and process recipe endpointing, the useof hydrogen, optical emission or hydrogen combined with a secondwavelength such as that of oxygen can also be used to monitor chamberhealth. In such an embodiment of the present invention, a detector unitmay be utilized with one or more bandpass filters coupled to thechamber. The oxygen emission peak(s) of 777 nm and/or 845 nm can also beutilized, either singly or jointly in combination with the hydrogenemission peak. The relative intensities of these peaks so measured andmonitored could be indicative of the conditions of the plasma sourcesand chamber surfaces and be used to provide a proper “fingerprint” of aclean or “golden” chamber. The magnitude of the emissions can be used todetermine when a cleaning cycle is necessary or whether componentswithin the chamber are degrading, i.e., certain emissions are indicativeof chamber health.

While foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

1. A method, comprising: positioning a substrate comprising a photoresist layer into a processing chamber; processing the photoresist layer using a multiple step plasma process; and monitoring the plasma for a hydrogen optical emission during the multiple step plasma process; wherein the multiple step plasma process comprises: removing a bulk of the photoresist layer using a bulk removal step; and switching to an overetch step in response to the monitored hydrogen optical emission.
 2. The method of claim 1, wherein the photoresist layer comprises a hardened crust layer.
 3. The method of claim 2, wherein the multiple step plasma process further comprises: etching the crust using a photoresist crust removal step and switching to the bulk removal step in response to the monitored hydrogen optical emission.
 4. The method of claim 3, further comprising: monitoring the plasma for an oxygen optical emission during the multiple step plasma process and switching to the bulk removal step in response to both the monitored hydrogen optical emission and the monitored oxygen optical emission.
 5. The method of claim 1, wherein the multiple step plasma process further comprises: switching to a residue removal step in response to the monitored hydrogen optical emission.
 6. The method of claim 5, further comprising: monitoring the plasma for an oxygen optical emission during the multiple step plasma process and switching to the residue removal step in response to both the monitored hydrogen optical emission and the monitored oxygen optical emission.
 7. The method of claim 1, wherein the hydrogen optical emission occurs at a wavelength of about 656 nm.
 8. The method of claim 1, further comprising: monitoring the plasma for an oxygen optical emission during the multiple step plasma process.
 9. The method of claim 8, wherein the oxygen optical emission occurs at a wavelength of about 777 nm.
 10. The method of claim 8, wherein the hydrogen optical emission is correlated with the oxygen optical emission.
 11. The method of claim 8, further comprising: stopping the multiple step plasma process upon either the hydrogen optical emission obtaining a first level or the oxygen optical emission obtaining a second level, or both.
 13. The method of claim 1, further comprising: stopping the multiple step plasma process upon the hydrogen optical emission obtaining a predetermined level.
 14. A method of etching a photoresist layer comprising: positioning a substrate comprising a photoresist layer into a processing chamber; processing the photoresist layer using a multiple step plasma process; and monitoring the plasma for both by-product optical emission and a reactant optical emission during the multiple step plasma process; wherein the multiple step plasma process comprises: removing a bulk of the photoresist layer using a bulk removal step; and switching to an overetch step in response to the monitored hydrogen optical emission.
 15. The method of claim 14, wherein the photoresist layer comprises a hardened crust layer.
 16. The method of claim 15, wherein the multiple step plasma process further comprises: etching the crust using a photoresist crust removal step and switching to the bulk removal step in response to the monitored by-product and reactant optical emissions.
 17. The method of claim 14, wherein the multiple step plasma process further comprises: switching to a residue removal step in response to the monitored by-product and reactant optical emissions.
 18. The method of claim 14, wherein the by-product is hydrogen.
 19. The method of claim 18, wherein the hydrogen optical emission occurs at a wavelength of about 656 nm.
 20. The method of claim 14, wherein the reactant is oxygen.
 21. The method of claim 20, wherein the oxygen optical emission occurs at a wavelength of about 777 nm.
 22. The method of claim 14, wherein the by-product optical emission is correlated with the reactant optical emission.
 23. The method of claim 14, further comprising: stopping the multiple step plasma process upon either the by-product optical emission obtaining a first level or the reactant optical emission obtaining a second level, or both. 